Multimedia systems in contemporary motor vehicles are designed as network systems which utilize optical or electrical bus systems based on ring topology. Key components (e.g., a control unit) whose internal structures are made up by a plurality of individual components (e.g., man-machine-interface-processor, tuner, gateway, etc.) may be interconnected in such a ring topology. For reasons of bus conformity, the mounting of these components in a housing requires a message and data exchange via the external bus, i.e., an internal data exchange between individual components which are independent of one another is not permissible. The components combined within one device act outwardly like separate logical devices.
If, in such a configuration, an internal gateway is connected to the interior CAN of the vehicle, e.g., via the CAN bus, then the relay of CAN messages to the internal components of the device and the communication between the components cease to take place in the event of failure of the external optical ring. Interruption of the ring thus causes complete failure of the system.
FIG. 2 shows the design of a known multimedia system for motor vehicles including an optical bus system 1 in the form of ring topology. D2B, MOST, or similar systems may be used here as bus systems common in motor vehicles. Additional components 3a through 3d are integrated into this optical ring.
A specific component 3d, explained here in greater detail, is optically coupled to optical bus system 1 via a connector system 2 which in turn is composed of a receiving module 4 and a transmitting module 5. Receiving module 4 receives optical signals from optical bus system 1 and converts them into electrical signals. Electrical signals are converted into optical signals in transmitting module 5 and are fed into ring 1.
The internal structure of interconnected component 3d having independent individual components 6 and 7 is schematically illustrated in FIG. 2. Component 6 has a transceiver 8 and a processor 9. In addition to transceiver 10 and processor 11, component 7 has an additional interface for exchanging data and commands with other common bus systems in the motor vehicle via lines CAN_H and CAN_L, implemented here as CAN bus interface 12, which is connected to processor 11 via bus B3. Line 22 is connected to an output STATUS of connector system 2 and signals activity (light) on optical ring 1 to processors 9 and 11 of internal components 6 and 7.
Optical signals from ring 1 are available as electrical signals at output RX_DATA of receiving module 4 on line 13 and are relayed to input 15 of transceiver 8 of component 6.
Using transceiver 8, processor 9 may pick up data and commands from the ring via bus B1 and feed them into input 18 of transceiver 10 via output 16 of transceiver 8 and line 17. Using transceiver 10, the data exchange from processor 11 takes place via bus B2, processor 11 feeding its data into input TX_DATA of the transmitting module via output 19 of transceiver 10 and line 21. Data and commands are available on ring 1 after electrical/optical conversion in transmitting module 5.
It is apparent in FIG. 2 that an electrical ring, composed of line 13, transceiver 8, line 17, transceiver 10, line 21, and connector system 2, exists after optical/electrical conversion by receiving module 4 and electrical/optical conversion by transmitting module 5 inside component 3d. 
If processor 11 receives data, which is intended for processor 9, via CAN interface 12 or if data exchange between processors 9 and 11 is to occur, this may only take place via optical ring 1, line 13, transceiver 8, line 17, transceiver 10, and line 21. The coupling point between the optical bus system and the electrical ring is formed by connector system 2. Data exchange between the internal components of the device ceases to take place if optical bus system 1 is interrupted or connector system 2 has faulty contacts. This results in complete failure of the device, even if the device could also be operated inside the device or via other motor vehicle-specific interfaces (e.g., CAN interface 12) without additional nodes from optical bus 1.
An object of the present invention is to provide a network component for an optical network including an emergency running function, in particular for an optical network based on ring topology, which ensures minimum emergency running properties (e.g., usability by the driver, error indicator, acoustic warning signals, maintenance of minimum (radio) functions) within the component in the event of interruption of the optical or electrical ring.